1. Technical Field
The present invention relates to a method for producing a tip unit for a liquid applicator such as a ball-point pen using water-based ink.
2. Background Art
A liquid applicator having a ball placed into its distal portion is conventionally known, wherein the ball transfers liquid, which adheres to the ball, onto the surface to be applied by being pressed. A typical example is a ball-point pen, which uses ink as the liquid. Inks of various kinds such as dyes or pigments dispersed in water, called “water-based inks” are known, as well as “water-based ball-point pens” containing such inks. “Water-based gel inks”, i.e., gelatinized inks are also used. Some ball-point pens using water-based gel ink can deliver a relatively large rate of ink.
The tip unit incorporated in the ball-point pen includes a ball for writing rotatively retained in a tip body, and while the ball-point pen is used, the ball rolls to transfer the ink from an ink reservoir to the writing surface such as a paper through the ball.
The known tip unit for the ball-point pen will be described:
Referring to FIG. 23, which is a cross-section showing the distal portion of a tip unit 120, the tip unit 120 is mainly composed of a tip body 100 and a ball 102. The distal portion of the tip body 100 is shaped like a truncated cone as shown in FIG. 23. The ball 102 is retained in a ball housing (a socket) 103, and is held by the distal end portion 101 of the tip body 100.
As shown in FIG. 23, the tip body 100 is provided with the ball housing 103 shaped in concave at its distal end, and a capillary hole 110 at its proximal end. The ball housing 103 is provided with a ball resting seat or merely seat 105 having a conical inner surface. The tip body 100 is further provided with ink channels 107 each communicating with the seat 105. The ink channels 107 secure smooth flow of liquid when the ball-point pen is used. The liquid flows toward the distal end portion 101 through the capillary hole 110 along the ink channels 107. This construction keeps the liquid flow even with the ball 102 pushed toward the seat 105 in using the ball-point pen, so as to apply the liquid.
The known method for producing the tip unit 120 will be described:
First, as shown in FIG. 20, the tip body 100 is internally and externally drilled and shaped into a predetermined shape, and then, the ball housing 103, the capillary hole 110, and the ink channels 107 are formed. Subsequently, as shown in FIG. 21, the ball 102 is placed into the ball housing 103. Finally, as shown in FIG. 22, the tip body 100 is pressed at its distal end portion 101 by pressers 114, the pressed distal end portion 101 being faced to the ball 102.
The next step is a “tapping,” wherein the ball 102 is lightly pressed down (or tapped) toward the seat 105 on its head. This tapping, as shown in FIG. 23, causes the surface of the seat 105 to be concave in compliance with the contour of the ball 102. As a result, in writing, the ball 102 is axially movable, thereby forming a gap S1 between the distal end portion 101 of the tip body 100 and the ball 102. The gap S1 is formed between the ball 102 and the open end of the tip body 100, so that the slightly heavier tapping makes the gap S1 wider. This fact is convenient for increasing the transfer of liquid.
In using the ball-point pen using the tip unit 120 for writing (applying), the ball 102 is pushed against a writing surface such as paper, running on the surface in accordance with moving of the pen, so that the liquid inside is applied onto the writing surface.
In the tip unit 120 tapped as described above, the ball 102 is axially movable, so as to tend to move backward along the axis by being pushed by the writing surface, in writing. Thus, in using the pen for writing onto the writing surface, the distal end portion 101 of the tip body 100 moves forward relatively to the ball 102 therein. As a result, the distal end portion 101 of the tip body 100 is likely to come into contact with the writing surface, resulting in scratching the writing surface and preventing from smoothly running on the writing surface, especially when the pen is in a slant position for the writing surface.
In order to avoid contact of the distal end portion 101 with the writing surface when the pen is held in a slant position for the writing surface, the distal end portion 101 of the tip body 100 must be thinned.
Reduction of the thickness of the distal end portion 101 avoids contact of the distal end portion 101 with the surface in a slant position of the pen, but it is difficult to machine the thin distal end portion 101 in the pressing process, and the pressing is likely to deform the portion needless to be deformed. Consequently, a method for producing a tip unit having a uniform and stable shape after pressing has been desired even when the distal end portion 101 is thin.
Especially, when the ball 102 has a small outer diameter, the distal end portion 101 must be more thinned; otherwise, the distal end portion 101 tends to come into contact with the writing surface in applying in a slant position. Thus, the smaller the outer diameter of the ball 102, the thinner the distal end portion 101 becomes, and therefore, the thin distal end portion 101 of the tip body 100 is difficult to be machined.
Furthermore, after the tip unit 120 is tapped, as described above, the ball 102 moves backward along the axis when the pen is used. At this stage, the gap S1 around the ball 102 becomes wider proportionally to the inclination of an inside surface K (FIG. 23) of the distal end portion 101 of the tip body 100 for the same amount of displacement to the backward of the ball 102. Therefore, in order to increase the rate of liquid discharge, the inclination of the inside surface K should be increased. In order to incline the inside surface K more, as shown in FIG. 22, it is necessary to make an angle of inclination of a portion to be deformed in the pressing process larger by using a presser 114 having a pressing surface 114a that has a larger inclination. However, this case has a problem in that a portion out of contact with the presser 114 may be undesirably deformed because of excessive deformation in the pressing process.
The present invention is directed to solve the difficulties discussed above, and to provide a method for readily producing a tip unit for a liquid applicator with the distal end portion 101 by a stable machining.